Manufacturers of integrated circuits (“ICs”) produce circuits in batches on a semiconductor substrate known as a wafer. Each individual circuit or device contained on a wafer is referred to as a “die.” A single wafer can contain a large number of individual die.
Generally, die are tested before being extracted from the wafer. Die are tested to isolate defects that could adversely affect the circuit's functionality and to ensure that the device performs adequately over a specified range of temperatures and/or voltages. Electrical testing of the die is sometimes performed by bringing a set of contacts or probes into electrical contact with the die being tested (i.e., the circuit under test). Some probes introduce electrical stimulus signals into the circuit under test. Additional probes detect electrical signals produced by the circuit under test in response to the stimulus signals. Die may be tested serially, or a number of die may be tested simultaneously.
The time required to test an integrated circuit directly affects the cost of producing the circuit. In some cases, the cost of testing an integrated circuit constitutes a substantial portion of the circuit's overall production cost. Further, the overall capacity of a production facility may be limited by the rate at which devices manufactured at the facility can be tested, requiring purchase of additional testers to alleviate the bottleneck. Thus, it is desirable to reduce the time required to test an integrated circuit.